PIPE FREEZERS USING EXPENDABLE REFRIGERANTS
A pipe freezer works by removing heat quickly enough from the liquid within a section of pipe that an ice plug forms in that section of pipe, thus effectively preventing the flow of liquid through that section of pipe. This ice plug acts as a temporary valve. When the ice plug is properly maintained (kept frozen), repairs can be performed on the pipe in the vicinity of the ice plug without the need to drain the piping system.
TWO PRIMARY METHODS OF FREEZING PIPES
1. Expendable refrigerants sprayed directly onto the pipe and vented to the atmosphere.
2. Compression cycle refrigeration, which circulates the same refrigerant in a closed loop as a refrigerator does.
1. Expendable refrigerants: These are the traditional refrigerants for freezing the contents (in a small section of pipe 5.08 cm-25.4 cm (2 in-10 in) in length) within plumbing piping or other fluid carrying conduits with a liquid that will freeze within the temperature range of the refrigerant being used.
The three more commonly used expendable refrigerants are listed below with their refrigerant number and boiling point at sea level (14.7 PSIA).
1. Liquid Carbon Dioxide: R744, -109 F. (-78 C)
2. Liquid Nitrogen: R728, -320 F. (-196 C)
3. Liquid Helium: R707, -425 F. (-269 C)
On pipes up to three 7.62 cm (three inches) of inner diameter the refrigerant of choice is carbon dioxide. There are five or more kits using carbon dioxide currently on the market in the US. Liquid nitrogen and liquid helium are not as available, are only packaged in large containers, and require additional safety training. There are companies that specialize in pipe freezing of pipes up to 152.4 cm (60 in) inside diameter. On pipes this large, liquid nitrogen or liquid helium would be used depending upon the application.
The current expendable refrigerant pipe freezing kits (for pipes up to 7.62 cm (3 in) ID) employ bags or collars that wrap around the pipe. The collars are hinged on one side and have a locking screw. The bags are wrapped around the pipe and tied on each end. Each type of kit has a spray head, which sprays the refrigerant over the pipe. A high-pressure hose delivers the liquid refrigerant to the spray heads from the tank.
As the liquid refrigerant is sprayed over the pipe within the bag or collar, dry ice is being formed due to the containment of the refrigerant (i.e., the refrigerant is not allowed to fully evaporate into the atmosphere). When enough dry ice is formed, the refrigerant valve on the tank is closed stopping the flow of refrigerant in to the bag or collar. To conserve refrigerant, heat is now removed from the pipe through the dry ice. The ability of the dry ice to remove heat from the pipe is much less than that of the denser liquid refrigerant. Throughout the process, the liquid refrigerant is turned on and off to conserve refrigerant, while depending on the dry ice, which was formed, to remove heat from the pipe.
Draw backs of free flow systems over Applicant's Multi-Cavity Adapter /Cartridge Evaporator
1. Requires longer freeze times.
2. Consumes more refrigerant
3. Cannot control vented gas location
4. Cost of equipment.
5. Danger of hose failure due to cold bending.